Along with Chenery, this man introduced a special 
Along with Chenery, this man introduced a special case production function that applies when the substitution effect is continually elastic. He later collaborated with Gerard Debreu to write a paper which proved the existence of a competitive equilibrium, which was crucial for GET. This author of The Limits of Organization later wrote Social Choice and Individual (*) Values, in which he advanced a theorem which can be extended with the addition of Pareto Optimality as a necessary condition. For 10 points, name this economist who posited that an intransitive social preference could not be derived from a set of transitive preferences, called his "Impossibility Theorem."
Along with Chenery, this man introduced a special case production function that applies when the substitution effect is continually elastic.
Kenneth {Arrow}